Conventionally, a parallel plate type plasma processing apparatus is widely employed as a plasma processing apparatus for performing a plasma processing such as an etching or a film forming process on a wafer serving as an object to be processed. The plasma processing apparatus includes a chamber serving as a vacuum processing vessel, and components such as an upper and a lower electrode, a susceptor, a focus ring and a shield ring are disposed in the chamber.
In the plasma processing apparatus, a processing gas is introduced into the chamber and, then, is converted into a plasma to generate radicals in, e.g., an etching process. By those radicals, components in the chamber and an inner wall of the chamber as well as a surface of the wafer are etched to be worn away. Further, the processing gas in the etching process contains a halogen element and, thus, the components in the chamber and the inner wall of the chamber tend to undergo an intensive corrosion. Accordingly, the components in the chamber and the inner wall of the chamber are formed of a wear resistant ceramic material, or a thermally sprayed ceramic coating is used on the surface thereof in order to prevent the wear and corrosion thereof.
Typically, the components in the chamber are attached to the inner wall of the chamber by using bolts for the maintenance and repair. The surface of the inner wall of the chamber is formed of a ceramic material as described above, so that a female screw portion for coupling to the bolt is formed in a ceramic portion. In this case, since the ceramic material is a brittle material, the female screw portion cannot be shaped accurately. Further, when an attachment bolt is made of, e.g., metal, there occurs galling between the bolt (male screw portion) and the female screw portion of the inner wall of the chamber. Thus, in the conventional plasma processing apparatus, the bolt is formed of a resin having elasticity and plasticity to prevent the galling. For example, as such a bolt, there is known a plastic bolt whose head and body made of a plastic material are in combination with each other (see, e.g., Japanese Utility Model No. 2579389)
However, since the plastic material is easily worn away by the radicals, the bolt (male screw portion) is worn away by the radicals that enter into a gap between the bolt (male screw portion) and the female screw portion of the inner wall of the chamber. Consequently, an axial force of the bolt is reduced such that the components in the chamber may fall apart.
A fluorine resin, e.g., PTFE, is known as a resin which is not worn away by the radicals, but the fluorine resin has a low hardness. Accordingly, the bolt made of fluorine resin is broken by a clamping torque, resulting in the degradation of the axial force to make the components fall apart.